The present invention relates to cooled stator blades or rotor blades for a gas turbine.
Such a flow deflection apparatus is generally known from the prior art, for example in the form of a cooled stator blade or rotor blade for a gas turbine.
Present-day flow deflection apparatus, especially stator blades or rotor blades in a gas turbine, are subjected to ambient temperatures which are above the maximum permissible material temperature. The use of special internal cooling channels reduces the metal temperature to a level which allows operation of such apparatus at high temperatures.
FIGS. 1 and 2 respectively show a cross section and longitudinal section of an example of a rotor blade of a gas turbine, as is currently used. The blade 10 essentially comprises a blade airfoil section 11 and a blade root 12, by means of which it is attached to the rotor of the gas turbine. A number of cooling channels 17 run in the longitudinal direction of the blade 10 in the interior of the (hollow) blade airfoil section 11, through which cooling channels 17 a cooling fluid, generally cooling air which enters through the blade root 12, flows. The cooling fluid runs, with a cooling effect, in the cooling channels 17 along the insides of the hot-gas walls 14 and then (for film cooling) emerges to the outside through appropriate film-cooling openings which are arranged on the leading edge 18, on the trailing edge 19 and at the blade tip (the emerging cooling fluid is indicated by the arrows in FIG. 2). The individual cooling channels 17 are separated from one another by separating walls 13 which at the same time have deflection devices 16 to ensure that the cooling fluid flows successively through adjacent cooling channels in alternately opposite directions.
Until now, and in this case specifically in the case of rotating guide apparatuses such as rotor blades, the cooling channels 17 and their separating walls 13 have been cast.
The known, cast separating walls 13 and deflection devices 16, which are also referred to as ribs, have a number of disadvantages, however:
The transitional region (15 in FIG. 1) from the hot-gas wall 14 to the separating wall (rib) 13 is an area which is difficult to cool owing to the large amount of material in that area. Increased heat transfer together with increased cooling-air consumption is required in order to ensure adequate strength there. The cold separating walls (ribs) 13, around which the cooling air flows, lead to thermal stresses with the hot-gas wall 14.
Casting of the internal channels leads to a high blade weight, which can lead to high centrifugal-force stresses both for the blade root 12 and for the blade airfoil section 11.
The complex casting lengthens casting development and increases the amount of scrap.
The object of the invention is thus to provide a cooled flow deflection apparatus which avoids the described disadvantages of the known apparatus and in particular is simple to produce, can be flexibly matched to the respective application, and is efficiently cooled.
The object is achieved by constructing the separating walls as separate inserts which are subsequently inserted into the apparatus, and are secured there. The invention is thus considerably different from solutions such as those described in U.S. Pat. No. 5,145,315 or U.S. Pat. No. 5,516,260, in which specific inserts in cast cooling channels are used for specific guidance of the cooling fluid.
The use of inserts (for example, in the case of blades, inserted through the blade root or through the blade tip) composed of metal or non-metal materials as a substitute for cast separating walls and, possibly, deflection devices, has a number of advantages:
There is no large amount of material in the transitional region from the hot-gas wall to the insert (to the separating wall).
There are no thermal stresses between the insert (separating wall) and the hot-gas wall.
In the case of rotating blades, the blade weight and thus the centrifugal-force stresses are reduced both in the blade root and in the blade airfoil section.
In the case of cast blades, the cast core is simpler, as a result of which both its capability to be produced and that of the blade are simpler.
The cooling system can easily be adjusted by replacing the inserts, for example by varying the deflection radius of deflection devices or by introducing connecting cross sections between two cooling channels.
A first preferred embodiment of the flow deflection apparatus according to the invention is characterized in that the flow deflection apparatus is in the form of a hollow casting, and in that holders, which are in the form of rails and into which the separating walls are inserted, are integrally formed in the interior of the flow deflection apparatus. This considerably simplifies assembly and attachment of the inserts, and ensures that the separating walls or inserts are sealed well at the edges. The separating walls are in this case preferably flat strips composed of a metallic or heat-resistant non-metallic (ceramic or composite) material.
A secure seating for the inserts is achieved if, according to a second preferred embodiment of the invention, the inserted separating walls are, for security, connected by an integral material joint, preferably by soldering or welding, to the flow deflection apparatus.
In the simplest form, the separating walls may be straight.
It is particularly simple and advantageous if, according to another embodiment, the cooling fluid flows in mutually opposite directions in two adjacent cooling channels, if the cooling fluid is deflected from the outlet of the one cooling channel into the inlet of the other cooling channel by means of a deflection device, and if the deflection is produced by a separating wall which is bent into a U-shape.
One particularly preferred embodiment of the flow deflection apparatus according to the invention is characterized in that the flow deflection apparatus is a blade in a gas turbine. Owing to the comparatively complex geometry of the blade, the invention in this case results in considerable simplifications.
Another embodiment, which is particularly advantageous for rotor blades which rotate at high speed, is characterized in that the cooling channels and separating walls extend essentially in the radial direction with respect to the rotation axis of the gas turbine, in that the inserted separating walls are, for security, connected by an integral material joint, preferably by soldering or welding, to the blade, and in that the integral material joint is arranged at the end of the separating walls close to the axis.